1) Field of the Invention
The present invention relates to a method of manufacturing products having a metal surface and more specifically, to methods and techniques for creating microstructures having microfeatures on the metal surface of products including metal foils, thin metal foils such as aluminum, heat exchangers and the like to impart properties to the foils including hydrophobic, superhydrophobic, hydrophillic, superhydrophillic, and oleophobicity.
2) Description of Related Art
Microstructured surfaces are known to have certain properties that do not exist in flat or non-microstructured surfaces For example, superhydrophobic surfaces easily repel water, and have further been shown to self-clean, mitigate ice formation, and reduce fouling properties. Superhydrophobic surfaces can also be created physically through the presence of microstructures formed on the surface of the material. These microstructures are generally formed at the 10−6 m scale and can trap a layer of air between themselves and a water drop. (It should be noted that the surface can still be hydrophobic even without a trapped air layer). The drop is prevented from sinking between the structures and is forced into an extreme contact angle with the surface. Water on these surfaces is extremely mobile and rolls away from the surface easily, carrying large dust particles and other contaminants with it. These surfaces have also been shown to repel more viscous fluids, such as honey or syrups.
Other properties that can be imparted to metal surfaces include providing hydrophobic (of water to exclude non-polar molecules, which leads to segregation of water and non-polar substances, to repel water), hydrophillic (capable of hydrogen bonding, enabling it to dissolve more readily in water than in oil or other hydrophobic solvents, to attract water), superhydrophillic, and oleophobic (repels oil).
While the prior art is replete with coating compositions and techniques, these techniques involve chemical processes to produce microfeatures on a metal surface. Unfortunately, there are many disadvantages to the use of chemical processes to modify a metal surface, including the inability to provide for consistently formed microfeatures. Once example of the disadvantages of chemical processes is illustrated in the publication titled Super-hydrophobic surface treatment as corrosion protection for aluminum in seawater, published in Corrosion Science on May 7, 2009. This publication describes that an underwater super-hydrophobic surface can be applied in the corrosion protection using melting myristic acid (CH3(CH2)12COOH) absorbed onto the anodized aluminum. However, use of acids and other chemicals, including myristic acid, complicates the manufacturing process by requiring specific storage techniques (keeping it away from heat and other sources of ignition), specific handling techniques (using a hood), and by posing a health risk as myristic acid can be harmful to humans in the case of ingestion, skin contact and eye contact. Further, degradation of products containing acids such as myristic acid occurs when stored for long terms.
An article titled Creating micro-scale surface topology to achieve anisotropic wettability on an aluminum surface published on Jun. 29, 2006 in Journal of Micromechanics and Microengineering, describes a technique for fabricating micropatterned aluminum surfaces with parallel grooves 30 μm wide and tens of microns in depth. Traditional photolithographic techniques were used to produce the surface features described in this publication. However, this technique only discloses the process for providing grooves in the surface and does not describe the creation of microstructures as in the present invention. Further, the surface features are two dimensional patterns and not the three dimensional patterns as can be achieved by the present invention, thereby significantly diminishing the physical properties that can be imparted onto a product with a metal surface. Further, the use of photolithographic and etching techniques do not lend themselves to mass production as required in industry, especially for the mass production of products such as aluminum foil.
Another technique still in development is to provide microfeatures created chemically by adding a coating. Significant disadvantages exist with using coating techniques, particularly with attempting to impart superhydrophobic properties since these coatings wear off easily, are costly to manufacture, often environmentally destructive and require expensive materials, special knowledge and special equipment, and cannot be applied to app materials. Coatings also are subject to strength of the bond between the coating and the underlying bulk material. Other alternatives to this invention are laser etching and material deposition. Both of these methods are costly, require specialized equipment, are limited as to material used, cannot be easily applied to large surface areas and require extreme precision, especially to create superhydrophobic surfaces.
Therefore, it is an object of this invention to apply microfeatures to a product having a metal surface, including thin metal foils such as aluminum or copper.
It is another object of the present invention to provide microstructures on the surface of thin metal foils to impart superhydrophobic properties to the material.
It is another object of the present invention to provide microstructures on the surface of thin metal foils in a cost effective, simplified and environmentally safe manner.